Intergranular Corrosion in High Purity Ferritic Stainless Steels: Isothermal Time-Temperature Sensitization Measurements

Abstract

Abstract Iosthermal sensitization heat treatments have been carried out on a high purity ferritic stainless steel (Fe-26% Cr) and the development of susceptibility to intergranular corrosion determined by means of the Huey test. It has been found that exposure to temperatures above 600 C (1110 F) does not cause a significant change in corrosion rates. Below this temperature, susceptibility to intergranular corrosion begins to develop. This sensitization increases in severity and reaches a maximum at longer times as the temperature is lowered. Isocorrosion (TTS) curves which are constructed on temperature versus log time graphs from the experimental data are analogous to those reported for austenitic stainless steels. This is discussed in terms of a common chromium depletion theory for the two classes of alloys. The sensitization which is found to develop after long times at temperatures near 475 C (885 F) is believed to be due to chromium depletion adjacent to the grain boundaries, rather than being assoc...